Gatekeeper Signaling
Cisco gatekeepers use H.323 RAS messages, the Attendant Update Agreement (GUP), and
the GKTMP as signaling methods back accouterment alarm services.
RAS is a subset of the H.225 signaling protocol. This signaling uses User Data Protocol
(UDP). Signaling letters amid gateways are H.225 alarm control, setup, or signaling
messages.
H.225 alarm ascendancy signaling is acclimated to set up access amid H.323 endpoints. The
ITU H.225 advocacy specifies the use and abutment of Q.931 signaling messages.
If no attendant is present, H.225 letters are exchanged anon amid endpoints.
As apparent in Figure 8-2, afterwards alarm signaling is set up amid gateways, H.245 is negotiated.
H.245, a ascendancy signaling agreement in the H.323 multimedia advice architecture,
is for the barter of end-to-end H.245 letters amid communicating H.323
endpoints. The H.245 ascendancy letters are agitated over H.245 ascendancy channels. The
H.245 ascendancy approach is the analytic approach 0 and is assuredly open, clashing the media
channels. The letters agitated accommodate letters to barter capabilities of terminals
and to accessible and abutting analytic channels.
446 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
V
V V
H.245 Media Ascendancy (TCP)
Dual RTP (UDP) Stream
Gateway
Gatekeeper
H.225 RAS (UDP) H.225 RAS (UDP)
Gateway
H.225 Alarm Bureaucracy (TCP)
UDP Anchorage Range:
16384–32767
Figure 8-2 Attendant Signaling
After a affiliation has been set up via the alarm signaling procedure, the H.245 alarm control
protocol is acclimated to boldness the alarm media blazon and authorize the media breeze before
the alarm can be established. It additionally manages the alarm afterwards it has been established.
As the alarm is set up amid gateways, all added anchorage assignments are dynamically negotiated,
as in the afterward examples:
■ RTP ports are adjourned from the everyman number.
■ The H.245 TCP anchorage is adjourned during H.225 signaling for a accepted H.323
connection.
■ The RTP UDP anchorage ambit is 16384–32767.